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Methodology Previous Releases
International comparison:
For more information on this release:
E-mail: environment@cso.ie Paul McElvaney (+353) 1 498 4150 Gerry Brady (+353) 1 498 4201
For general information on CSO statistics:
information@cso.ie (+353) 21 453 5000 On-line ISSN 2737-7555
CSO statistical release, , 11am

Plant Phenology

2020

Table A: Number of observations by garden by phenophase 1966-2020
Number of observations
StationBeginning of leaf unfoldingMay shootBeginning of floweringGeneral floweringFirst ripe fruitsAutumn colouringLeaf fall Total
Enniscoe House517484345157 261
Glenveagh National Park1611856324160169 600
John F. Kennedy Arboretum4851243417723210328 1,588
Johnstown Castle39810217814655317402 1,598
National Botanic Gardens4391011083..314428 1,393
Valentia Observatory5668430822229360496 2,065
          
Total2,1004361,0395231151,4121,880 7,505
.. Not available

Wide variability in timing and length of phenological season

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The length of the phenological season for Downy Birch (Betula pubescens) at Valentia Observatory in Kerry during the period 1969-2020 varied from 168 days in 1979 to 236 days in 2014 (see Figure 1). The length of the phenological season is defined as the number of days between beginning of leaf unfolding in the Spring and leaf fall in the Autumn. The Met Éireann observers at Valentia Observatory have a full record for this plant species for the 51 year period.

The earliest date for leaf unfolding of Downy Birch at Valentia Observatory was day 72 or the 13th March 1975. The latest date for beginning of leaf unfolding was 24th April in both 1979 and 1986. For leaf fall, the earliest date at Valentia Observatory for Downy Birch was day 268 or 25th September 1983 and the latest date was day 330 or 26th November 2014. The earliest dates for each phenophase stage for Downy Birch in each garden are given in Table 1.02.

The length of the phenological season for Alpine Currant (Ribes alpinum) at the National Botanic Gardens in Dublin varied from 202 days in 2016 to 258 days in 1997 (see Figure 2).

The earliest date for beginning of leaf unfolding of Small-leaved Lime (Tilia cordata) at Johnstown Castle in Wexford was day 70 or the 11th March 2019 (see Figure 3). The latest date for beginning of leaf unfolding of Small-leaved Lime (Tilia cordata) at Johnstown Castle was day 132 or the 12th May 1979. For leaf fall, the earliest date at Johnstown Castle for Small-leaved Lime was day 273 or 30th September 2015 and the latest date was day 321 or the 16th November 2016 (see Table 1.10).

The earliest date for general flowering for Wild Cherry (Prunus avium) at Enniscoe House in County Mayo was at 103 days or 13th April in both 2015 and 2019 (see Figure 4 and Table 1.07). 

Phenology is the study of annual seasonal changes in plants and animals. Plant phenology has been proposed as an indicator of climate change by the Intergovernmental Panel on Climate Change.
The data used for this release were provided by Met Éireann and the National Botanic Gardens.

See Infographic

The earliest date for beginning of leaf unfolding of European Larch (Larix decidua) at Glenveagh National Park in Donegal was day 86 on the 27th March 2009 and the 26th March 2012 (see Figure 5). The latest date for beginning of leaf unfolding was day 114 or the 24th April 2018. For leaf fall, the earliest date at Glenveagh National Park for European Larch was day 299 or 26th October 2018 and the latest date was day 321 or the 17th November 2009 (see Table 1.01).

The earliest date for beginning of leaf unfolding of European Beech (Fagus sylvatica (Trippstadt)) at John F. Kennedy Arboretum in Wexford was day 110 on the 20th April 1993 (see Figure 6). The latest date for beginning of leaf unfolding was day 137 or the 17th May 1970 and 17th May 1974. For leaf fall, the earliest date at John F. Kennedy Arboretum for European Beech was day 277 or 4th October 1991 and the latest date was day 322 or the 17th November 1976 and the 18th November 1985 (see Table 1.05).

X-axis labelBetula pubescens (Germany) LPS
1969218
1970198
1971194
1972202
1973196
1974190
1975222
1976225
1977187
1978182
1979168
1980181
1981231
1982200
1983181
1984187
1985188
1986183
1987187
1988195
1989222
1990197
1991218
1992205
1993213
1994218
1995200
1996225
1997203
1998217
1999215
2000217
2001203
2002200
2003201
2004208
2005199
2006210
2007175
2008228
2009223
2010207
2011201
2012192
2013230
2014236
2015233
2016212
2017217
2018206
2019231
2020215
X-axis labelRibes alpinum (Austria) LPS
1976211
1977208
1978211
1979210
1980214
1981213
1982216
1983210
1984213
1985215
1986212
1987215
1988225
1989227
1990236
1991234
1992224
1993
1994231
1995
1996
1997258
1998248
1999221
2000216
2001
2002240
2003241
2004235
2005236
2006232
2007238
2008235
2009248
2010
2011222
2012239
2013229
2014
2015241
2016202
2017228
2018216
2019244
2020
Leaf Unfolding StageLeaf Fall Stage
1970125null
1971119null
1972128null
1973125276
197494291
1975123null
1976127280
1977124304
1978131321
1979132316
1980nullnull
1981nullnull
1982105null
1983106null
1984107317
1985107316
1986104316
1987105314
198890304
1989104298
199096315
1991103307
1992102311
199395310
1994101308
1995106306
1996105297
1997104277
1998106285
1999nullnull
200098302
2001nullnull
2002nullnull
2003nullnull
2004nullnull
2005nullnull
2006nullnull
2007nullnull
2008nullnull
2009nullnull
2010nullnull
2011124306
201290293
2013122289
2014101303
201583273
2016111321
201789292
2018106319
201970288
202090276
X-axis labelPrunus avium (Bovenden) (Germany) FF
2013114
2014
2015103
2016119
2017114
2018117
2019103
2020107
X-axis labelLeaf Unfolding stageLeaf Fall stage
2007306
200891316
200986321
201098309
201190308
201286320
2013113316
2014105309
2015106311
2016110308
2017103309
2018114299
201998308
2020101304
X-axis labelFagus sylvatica (Trippstadt) (Germany) UL
1970137
1971127
1972136
1973135
1974137
1975122
1976122
1977129
1978129
1979134
1980127
1981128
1982125
1983129
1984121
1985126
1986132
1987124
1988130
1989
1990121
1991130
1992118
1993110
1994122
1995130
1996130
1997121
1998
1999123
2000126
2001125
2002127
2003122
2004131
2005129
2006128
2007123
2008135
2009128
2010132
2011119
Table 1.01 Date of Earliest Occurrence of Phenological Stages for 111 Larix decidua* (Germany)
 Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
Enniscoe House8420161162016126201627020163082016
Glenveagh National Park862009........29620182992018
.. Not available
Table 1.02 Date of Earliest Occurrence of Phenological Stages for 211 Betula pubescens* (Germany)
 Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
Glenveagh National Park872012902017113201928120152932015
John F. Kennedy Arboretum851992941997109199326419962741991
Johnstown Castle602019802019100201915120182752019
National Botanic Gardens801977........29619923111992
Valentia Observatory7219751051976112198525519832681983
.. Not available
Table 1.03 Date of Earliest Occurrence of Phenological Stages for 221 Fagus sylvatica (Hardegsen)* (Germany)
Beginning of leaf unfoldingAutumn colouringLeaf fall
StationDayYearDayYearDayYear
Enniscoe House93201327820183052016
Glenveagh National Park109202024820182622018
John F. Kennedy Arboretum94200726019942751974
Johnstown Castle91197425819762831973
National Botanic Gardens118199729319943181997
Valentia Observatory79201124819832561971
Table 1.04 Date of Earliest Occurrence of Phenological Stages for 222 Fagus sylvatica (Düdelsheim) (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringFirst ripe fruitsAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYearDayYear
Glenveagh National Park652008............26320132532019
John F. Kennedy Arboretum1041993............26519922691971
Johnstown Castle7820199720161072016218201624520192752020
Valentia Observatory1002008............24820052671974
.. Not available
Table 1.05 Date of Earliest Occurrence of Phenological Stages for 223 Fagus sylvatica (Trippstadt) (Germany)
Beginning of leaf unfoldingAutumn colouringLeaf fall
StationDayYearDayYearDayYear
John F. Kennedy Arboretum110199327219912771991
Johnstown Castle117197828519773001977
National Botanic Gardens118199928420043012005
Valentia Observatory92200824119862301971
Table 1.06 Date of Earliest Occurrence of Phenological Stages for 235 Populus tremula* (Germany)
Beginning of leaf unfoldingAutumn colouringLeaf fall
StationDayYearDayYearDayYear
Glenveagh National Park100201127120112922009
John F. Kennedy Arboretum92198127819902781987
Johnstown Castle92197729219882791973
National Botanic Gardens105201128620092952009
Valentia Observatory80201726420102642009
Table 1.07 Date of Earliest Occurrence of Phenological Stages for 241 Prunus avium (Bovenden)* (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringFirst ripe fruitsAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYearDayYear
Enniscoe House7820199620191032015....25120152792015
Glenveagh National Park822012882012982019....26420082762008
John F. Kennedy Arboretum7819929519901061988199197727819852791986
Johnstown Castle652019872019932019168201624420192672019
National Botanic Gardens591976841990951990....28419763032016
Valentia Observatory722008851991941989195198223019802551983
.. Not available
Table 1.08 Date of Earliest Occurrence of Phenological Stages for 242 Prunus avium (Lutter) (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringFirst ripe fruitsAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYearDayYear
Glenveagh National Park1012010....................
John F. Kennedy Arboretum851992882002912011203197610620012781981
Johnstown Castle73199710319771111977184197626219982801997
National Botanic Gardens581981831990941990....28419813111976
Valentia Observatory752008841989921982193198224220052551983
.. Not available
Table 1.09 Date of Earliest Occurrence of Phenological Stages for 271 Sorbus aucuparia* (Czech Rep.)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringFirst ripe fruitsAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYearDayYear
Enniscoe House8320209420131092013....25820152782018
Glenveagh National Park91201912120201252020241201426120082502011
John F. Kennedy Arboretum94201111219911141991213200228220092841983
Johnstown Castle72201910620191402016215201624520192801976
National Botanic Gardens9619891231989........28519893051991
Valentia Observatory90199410319991171997194201025720052542007
.. Not available
Table 1.10 Date of Earliest Occurrence of Phenological Stages for 281 Tilia cordata* (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringFirst ripe fruitsAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYearDayYear
Glenveagh National Park1012011............28720092932009
John F. Kennedy Arboretum10619741181987........27820002872000
Johnstown Castle70201910420151202015131201724420152732015
National Botanic Gardens1121972............27819763131994
Valentia Observatory901993............22719832401983
.. Not available
Table 1.11 Date of Earliest Occurrence of Phenological Stages for 311 Ribes alpinum* (Austria)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
John F. Kennedy Arboretum751983701997832003....2941983
Johnstown Castle7519931031968116197727419992831997
National Botanic Gardens791997861991....29219893072016
Valentia Observatory11919741161971........2691974
.. Not available
Table 1.12 Date of Earliest Occurrence of Phenological Stages for 321 Salix aurita* (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
Enniscoe House4620179201751201726720172942016
Glenveagh National Park11320191132018122201828120152742014
John F. Kennedy Arboretum1061993891990103199531420063041984
Johnstown Castle50201939201753201725220202812020
National Botanic Gardens1111997951992....29019893151992
Valentia Observatory85200561201772201728020062791974
.. Not available
Table 1.13 Date of Earliest Occurrence of Phenological Stages for 323 Salix acutifolia* (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
Enniscoe House8120169201734202027420193042013
Glenveagh National Park952011832009....27520082792008
John F. Kennedy Arboretum572004131993391988....3071983
Johnstown Castle77199365197192197827920002811973
National Botanic Gardens10119881031982....30619893191981
Valentia Observatory71200854201761201727320092801974
.. Not available
Table 1.14 Date of Earliest Occurrence of Phenological Stages for 324 Salix smithiana* (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
Glenveagh National Park86201272201190201728720092982009
John F. Kennedy Arboretum67200428199353198531420063051980
Johnstown Castle37201938201752201724620192772012
National Botanic Gardens872019601974....28220163141976
Valentia Observatory61201150199359201728919972791974
.. Not available
Table 1.15 Date of Earliest Occurrence of Phenological Stages for 326 Salix viminalis* (Germany)
Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
Enniscoe House6320139201741202027420133062016
Glenveagh National Park94201484201790201730520123162018
John F. Kennedy Arboretum65200611199335198827720082971984
Johnstown Castle42201944201759201724620192752020
National Botanic Gardens882019781973....32020123161976
Valentia Observatory77199647198267197528120052801974
.. Not available
Table 1.16 Date of Earliest Occurrence of Phenological Stages for 411 Corylus avellana*
Beginning of leaf unfoldingBeginning of floweringGeneral floweringFirst ripe fruitsAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYearDayYear
Enniscoe House33201712018152018267202025620162702016
Glenveagh National Park912009112019492015....26720192982009
John F. Kennedy Arboretum942007422010462010....30920063192006
Johnstown Castle732019322019482017137201827720173132017
National Botanic Gardens522019............29720193242020
Valentia Observatory692019............28920173042017
.. Not available
Table 1.17 Date of Earliest Occurrence of Phenological Stages for 431 Syringa x chinensis (Red Rothomagensis)*
Beginning of leaf unfoldingBeginning of floweringGeneral floweringAutumn colouringLeaf fall
StationDayYearDayYearDayYearDayYearDayYear
Enniscoe House................3332013
Glenveagh National Park5720081182020126202025920082752008
John F. Kennedy Arboretum7920091072007117200728920083222006
Johnstown Castle6920201202018136201827520172992017
Valentia Observatory652019962011....27520172892011
.. Not available

Background Notes

Introduction

Phenology is the study of annual seasonal changes in plants and animals such as the flowering of plants, the emergence of insects and the migration of birds. Phenology has been principally concerned with the dates of first occurrence of biological events in their annual cycle. Examples include the date of emergence of leaves and flowers, the first flight of butterflies, the first appearance of migratory birds, the date of leaf colouring and leaf fall in deciduous trees, the dates of egg-laying of birds, etc. Because many such phenomena are very sensitive to small variations in climate, phenological records can be a useful proxy for temperature in historical climatology, especially in the study of climate change. Changes in timing affect ecosystem functioning. Plant phenology has been proposed as an indicator of climate change by the European Environmental Agency and the Intergovernmental Panel on Climate Change. Changes in the timing of phenological events may influence biological processes and species distribution.

Data Sources

The data used for this release were obtained directly from Met Éireann and the National Botanic Gardens. The CSO integrated the annual observations from each garden into one integrated file. The full time-series of available data back to 1966 has been used.

Observation

In this report, an observation is defined as a single date for one phenological stage for one tree at one location. In some cases, multiple dates were available for the same event e.g. where a plant was cloned at the same garden. If the observer had combined the cloned observations into a single date for the phenophase then that was used. The number of observations recorded per station and per phenophase is shown in Table A. An example of a Phenological Observations Sheet can be found on the Methodology section of this release here: Methodology

Revisions and Errors

Some phenological events must precede other events. However there are known errors in the microdata used for this report. These errors have not been corrected. It is hoped that it may be possible to recheck some of the data or to obtain access to the original data.

Length of the Phenology Season

The number of days between the beginning of leaf unfolding and leaf fall dates has been used in some graphs as an approximation for the length of the growing season.

CSO PxStat Database

The full time series of observations has been made available on the CSO PxStat database. Users should note that the series has not been smoothed to correct errors in the observation dates.

Phenophases

Beginning of leaf unfolding (bud burst): This phase occurs when the first regular surfaces of leaves become visible in three to four places. This is when the first leaf of a plant has pushed out of the bud up to its leaf stalk.

May shoot: This is the first spring sprout of the conifers. The buds are open and the protective sheath comes off the bud edges. The needles have not yet expanded at this point. 

Beginning of flowering: This is when the first regular flowers have opened in three to four places on the observed plant.

General flowering: This occurs when more than half of the blossoms are open.

St John’s sprout: The first sprouts of oaks and mountain ashes are regularly followed by a second sprout, the St John’s sprout. Buds that are already developed for the next year are caused to sprout prematurely by weather conditions. These second sprouts can be recognised by their fresh colour. The state of the first leaf unfolding is repeated: the first leaves of the sprout have their typical forms but not yet the final size of the fully developed leaves.

First ripe fruits: This phase is observed when the first fruits have ripened in several places (about three or four) on the observed plant.

Autumn colouring: More than half of the leaves of the observed plant have changed their colour, including those leaves which have fallen in large quantities.

Leaf fall: This is recorded when more than half of the leaves of the observed plant have fallen.

International Phenological Gardens of Europe

The International Phenological Gardens is a network of gardens that was formed to record standardised phenological observations. All IPGs are situated in similar surroundings (mainly plain surface with meadows and some trees). Data are collected using a detailed observation-guide. In order to eliminate the hereditary variability, cloned species of all trees and shrubs have been planted in the IPGs. To enable this, a parent garden doing the vegetative propagation, breeding, and dispatch was established. The IPG network in Ireland has four sites (Valentia Observatory (Co. Kerry), John F. Kennedy Arboretum (Co. Wexford), Johnstown Castle (Co. Wexford) and the National Botanic Gardens (Dublin)) with phenological data records extending as far back as 1966. Observers record and monitor phenophases such as leaf unfolding, flowering, leaf fall, etc. for a range of species.

Irish Phenological Gardens

Observations from six Irish gardens were available for inclusion in this report:

- Data for Enniscoe House in Mayo (West) for 2013-2020 were used in this report (8 years)
- Data for Glenveagh National Park in Donegal (North-West) for 2007-2020 were used in this report (14 years)
- Data for John F. Kennedy Arboretum in Wexford (South-East) for 1967-1988 and 1990-2011 were used in this report (44 years)
- Data for Johnstown Castle in Wexford (South-East) for 1967-1979, 1982-2000, and 2011-2020 were used in this report (42 years)
- Data for National Botanic Gardens in Dublin (East) for 1966-1974, 1976-1992, 1994, 1997-2009, and 2011-2020 were used in this report (50 years)
- Data for Valentia Observatory in Kerry (South-West) for 1966-2020 were used in this report (55 years)

Pan European Phenology Project

The main objective of PEP725 is to promote and facilitate phenological research by delivering a pan European phenological database with open data access for science, research and education purposes.

Plant species

The records maintained at Irish gardens include the following species:

CodePlant species nameEnglish name
[111] Larix decidua* (Germany) European larch
[112] Larix decidua (E-France) European larch
[113] Larix decidua (S-Poland) European larch
[114] Larix decidua (Czech Republic) European larch
[115] Larix decidua (N-Italy) European larch
[121] Picea abies (early)* (Germany)  Norway spruce 
[122] Picea abies (late)* (Germany)  Norway spruce 
[123] Picea abies (northern) (Norway)   Norway spruce 
[124] Picea abies (late) (E-Poland)   Norway spruce 
[125] Picea abies (average) (E-Poland)  Norway spruce 
[126]  Picea abies (E-Germany) Norway spruce
[127]  Picea abies (E-France) Norway spruce
[128]  Picea abies (N-Scandinavia) Norway spruce
[129]  Picea omorika (Croatia) Serbian spruce
[131]  Pinus sylvestris* (Poland) Scots pine
[132]  Pinus sylvestris (E-France) Scots pine
[133]  Pinus sylvestris (N-Scandinavia)  Scots pine
[211]  Betula pubescens* (Germany) Downy birch
[215]  Betula pendula (N-Poland) Silver birch
[216]  Betula pendula (N-Scandinavia) Silver birch
[221]  Fagus sylvatica (Hardegsen)* (Germany) European beech
[222]  Fagus sylvatica (Düdelsheim) (Germany) European beech
[223]  Fagus sylvatica (Trippstadt) (Germany)  European beech
[224]  Fagus sylvatica (Denmark) European beech
[226] Fagus orientalis (Balkan) Oriental beech
[231] Populus canescens (Germany)  Grey poplar
[235] Populus tremula* (Germany) European aspen
[236] Populus tremula (E-Poland)  European aspen
[237] Populus tremula (S-Finland) European aspen
[238] Populus tremula (Ireland) European aspen
[239] Populus tremula (Greece) European aspen
[241] Prunus avium (Bovenden)* (Germany)  Wild cherry
[242] Prunus avium (Lutter) (Germany) Wild cherry
[251] Quercus petraea (Zell/Mosel) (Germany)  Sessile oak
[253] Quercus petraea (Croatia)  Sessile oak
[256] Quercus robur (Wolfgang)* (Germany)  Pedunculate oak
[257] Quercus robur (Barlohe) (Germany)  Pedunculate oak
[258] Quercus robur (Croatia) Pedunculate oak
[261] Robinia pseudoacacia* (USA)  Black locust
[271] Sorbus aucuparia* (Czech Rep.) Rowan / Mountain ash
[272] Sorbus aucuparia (N-Scandinavia)  Rowan / Mountain ash
[281] Tilia cordata* (Germany)  Small-leaved lime
[311] Ribes alpinum* (Austria)  Alpine currant
[321] Salix aurita* (Germany) Eared willow
[323] Salix acutifolia* (Germany) Siberian violet-willow
[324] Salix smithiana* (Germany)  Silky-leaf osier
[325] Salix glauca (Greenland) Grayleaf willow
[326] Salix viminalis* (Germany)  Osier willow
[331] Sambucus nigra* (Germany) Elder
[411] Corylus avellana* Common hazel
[421] Forsythia suspensa (Fortunei)* Weeping forsythia
[431] Syringa x chinensis (Red Rothomagensis)*  Chinese lilac
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